Dynamic current steering mixer

ABSTRACT

A dynamic current steering mixer. The dynamic current steering mixer comprises a Gilbert cell mixer core, a pair of load devices, a dynamic current steering cell, and a transconductor cell. The Gilbert cell mixer core has first and second nodes, receives a first differential input signal, and provides a differential output signal at the first nodes thereof. The load devices are respectively coupled between the first nodes of the Gilbert cell mixer core and a first fixed voltage. The dynamic current steering cell has third nodes coupled to the second nodes and fourth nodes. The transconductor cell is coupled between the fourth nodes and a second fixed voltage and receives a second differential input signal. The dynamic current steering cell alternately steers current of the transconductor cell to or away from the Gilbert cell mixer core.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.11/697,347, filed on Apr. 6, 2007 and entitled “DYNAMIC CURRENT STEERINGMIXER”, now U.S. Pat. No. 7,725,092, the entirety of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a double-balanced mixer and, in particular, toa double-balance mixer with a dynamic current steering cell.

2. Description of the Related Art

Mixer circuits for high frequency applications constructed using metaloxide semiconductor (MOS) transistors are subject to a limited voltagesupply (usually less than 2V) and high levels of flicker noise, havingfrequencies extending to several tens of MHz. Accordingly, the gain andoutput signal level required in such mixer circuits exceed thoserequired in the equivalent bipolar circuits.

FIG. 1 is a circuit diagram illustrating a conventional double balancedmixer circuit. The double balanced mixer circuit in FIG. 1 includesdifferential pairs of MOSFETs (Q131-Q132 and Q133-Q134). The drains ofthe pairs of MOSFETs are connected to an output terminal (Output-I⁺ andOutput-I⁻). The gates of the pairs of MOSFETs are connected to firstinput terminals (Input-II⁺ and Input-II⁻). The double balanced mixercircuit in FIG. 1 also includes active devices Q135, Q136, Q137 andQ138. The sources of the MOSFET pair Q131-Q132 are connected to thedrains of the active devices Q135 and Q136. The sources of the MOSFETpair Q133-Q134 are connected to the drains of the active devices Q137and Q138. The gates of the active devices Q135, Q136, Q137 and Q138 areconnected to the second input terminal (Input-I⁺ and Input-I⁻). Thesources of the active devices Q135, Q136, Q137 and Q138 are connected tothe ground through an impedance unit (Degeneration Impedance).

FIG. 2 is a circuit diagram of a conventional quadrature mixer disclosedby Raja S Pullela et. al in ISSCC 2006. The conventional quadraturemixer 200 comprises an I-Mixer Quad 210, a Q-Mixer Quad 220, a 2× LOstage 230, and a transconductor stage 240. The I-Mixer Quad 210 in FIG.2 includes differential pairs of MOSFETs (M9-M10 and M11-M12). Thedrains of the pairs of MOSFETs are connected to an output terminal (BBIpand BBIn). The gates of the pairs of MOSFETs are connected to firstinput terminals (LOIp and LOIn). The Q-Mixer Quad 220 in FIG. 2 includesdifferential pairs of MOSFETs (M13-M14 and M15-M16). The drains of thepairs of MOSFETs are connected to an output terminal (BBQp and BBQn).The gates of the pairs of MOSFETs are connected to first input terminals(LOQp and LOQn). The 2× LO stage 230 comprises MOSFETs M5, M6, M7 andM8. Sources of the MOSFETs M9-M10 and M11-M12 are respectively connectedto drains of the MOSFETs M5 and M7 and those of the MOSFETs M13-M14 andM15-M16 respectively connected to drains of the MOSFETs M6 and M8. Gatesof the MOSFETs M5 and M7 are connected to an input terminal 2Lop andthose of the MOSFETs M6 and M8 connected to an input terminal 2Lon.MOSFETs M1 and M3 are connected between the sources of the MOSFETs M5-M6and a ground GND and MOSFETs M2 and M4 connected between the sources ofthe MOSFETs M7-M8 and the ground. Gates of the MOSFETs M1 and M3 areconnected to an input terminal RF+ and those of the MOSFETs M2 and M4connected to an input terminal RF−.

BRIEF SUMMARY OF THE INVENTION

An embodiment of a dynamic current steering mixer comprises a Gilbertcell mixer core, a pair of load devices, a dynamic current steeringcell, and a transconductor cell. The Gilbert cell mixer core has firstand second nodes, receives a first differential input signal, andprovides a differential output signal at the first nodes thereof. Theload devices are respectively coupled between the first nodes of theGilbert cell mixer core and a first fixed voltage. The dynamic currentsteering cell has third nodes coupled to the second nodes and fourthnodes. The transconductor cell is coupled between the fourth nodes and asecond fixed voltage and receives a second differential input signal.The dynamic current steering cell alternately steers current of thetransconductor cell to or away from the Gilbert cell mixer core.

An embodiment of a quadrature dynamic current steering mixer comprisesfirst and second dynamic current steering mixers connected in parallelbetween first and second fixed voltages. Each of the first and seconddynamic current steering mixers comprises a Gilbert cell mixer core, apair of load devices, a dynamic current steering cell, and atransconductor cell. The Gilbert cell mixer core has first and secondnodes, receives a first differential input signal, and provides adifferential output signal at the first nodes thereof. The load devicesare respectively coupled between the first nodes of the Gilbert cellmixer core and the first fixed voltage. The dynamic current steeringcell has third nodes coupled to the second nodes and fourth nodes. Thetransconductor cell is coupled between the fourth nodes and the secondfixed voltage and receives a second differential input signal. Thedynamic current steering cell alternately steers current of thetransconductor cell to or away from the Gilbert cell mixer core. Thereis a phase difference of 90° between the first differential inputsignals of the first and second dynamic current steering mixers.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a circuit diagram illustrating a conventional double balancedmixer circuit;

FIG. 2 is a circuit diagram of a conventional quadrature mixer disclosedby Raja S Pullela et. al in ISSCC 2006;

FIG. 3 is a circuit diagram of a dynamic current steering mixeraccording to an embodiment of the invention;

FIG. 4A is a detailed circuit diagram of the dynamic current steeringmixer in FIG. 3;

FIG. 4B is a schematic diagram showing waveforms of the local oscillatorsignal LO+/LO− and the control signal 2 fo in FIG. 4A;

FIG. 4C is a detailed diagram of a variant of the dynamic currentsteering mixer in FIG. 4A;

FIG. 4D is a detailed diagram of another variant of the dynamic currentsteering mixer in FIG. 4A;

FIG. 5A is a detailed circuit diagram of the dynamic current steeringmixer in FIG. 3;

FIG. 5B is a schematic diagram showing waveforms of the local oscillatorsignal LO+/LO− and the control signal 2 fo in FIG. 5A;

FIG. 5C is a detailed diagram of a variant of the dynamic currentsteering mixer in FIG. 5A;

FIG. 5D is a detailed diagram of another variant of the dynamic currentsteering mixer in FIG. 5A;

FIG. 6A is a schematic diagram of current of a Gilbert cell mixer corein a conventional double balanced mixer and a dynamic current steeringmixer according to an embodiment of the invention;

FIGS. 6B and 6C are respectively schematic diagrams of current of theNMOS transistors in a Gilbert cell mixer core of a conventional doublebalanced mixer and a dynamic current steering mixer according to anembodiment of the invention;

FIG. 6D is a schematic diagram showing noise figure of a conventionaldouble balanced mixer and a dynamic current steering mixer according toan embodiment of the invention;

FIG. 7A is a circuit diagram of a quadrature dynamic current steeringmixer according to an embodiment of the invention;

FIG. 7B is a schematic diagram showing waveforms of the local oscillatorsignals LOIP/LOIN and LOQP/LOQN and the control signals 2LOP and 2LON;

FIG. 8A is a circuit diagram of a variant of the quadrature dynamiccurrent steering mixer according to an embodiment of the invention; and

FIG. 8B is a circuit diagram of a variant of the quadrature dynamiccurrent steering mixer in FIG. 8A.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FIG. 3 is a circuit diagram of a dynamic current steering mixeraccording to an embodiment of the invention. The dynamic currentsteering mixer 300 comprises a Gilbert cell mixer core 310, a pair ofload devices RL, a dynamic current steering cell 330, and atransconductor cell 350. The Gilbert cell mixer core 310 has first nodes311 and 311′ and second nodes 313 and 313′ and comprises differentialpairs of NMOS transistors T7-T8 and T9-T10 coupled therebetween. TheGilbert cell mixer core 310 receives a local oscillator signal LO+/LO−,and provides an intermediate frequency (IF) signal IF+/IF− at the firstnodes 311 and 311′. The load devices RL are respectively coupled betweenthe first nodes 311 and 311′ of the Gilbert cell mixer core 310 and asupply voltage Vcc. The dynamic current steering cell 330 has thirdnodes 331 and 331′ respectively coupled to the second nodes 313 and313′, and fourth nodes 333 and 333′. The dynamic current steering cell330 comprises a first switch 335 and a second switch 335′. The first andsecond switches 335 and 335′ alternately connect to the fourth nodes 333and 333′, the third node 331 and 331′, and a fixed voltage Vdd accordingto a control signal 2 fo, respectively. Frequency of the control signalis twice of that of the local oscillator signal LO+/LO−. Thetransconductor cell 350 comprises NMOS transistors T1 and T2 coupledbetween the fourth nodes 333 and 333′ and a ground GND. Gates of theNMOS transistors T1 and T2 receive a radio frequency (RF) signalRF+/RF−.

FIG. 4A is a detailed circuit diagram of the dynamic current steeringmixer in FIG. 3. In FIG. 4A, the dynamic current steering cell 330comprises NMOS transistors T3, T4, T5 and T6. The NMOS transistors T3and T6 are coupled between the third nodes 331 and 331′ and the fourthnodes 333 and 333′. The NMOS transistors T4 and T5 are coupled betweenthe fixed voltage Vdd and the fourth nodes 333 and 333′. Gates of theNMOS transistors T3 and T6 receive the control signal 2 fo and those ofthe NMOS transistors T4 and T5 are connected to a reference voltageVref. Preferably, the fixed voltage Vdd is the same as the supplyvoltage Vcc. FIG. 4B is a schematic diagram showing waveforms of thelocal oscillator signal LO+/LO− and the control signal 2 fo in FIG. 4A.At zero-crossing points Toff of the local oscillator signal LO+/LO−,voltage level of the control signal 2 fo is lower than the referencevoltage Vref, allowing the NMOS transistors T3 and T6 to be turned off.Current (both DC and AC) of the transconductor cell 350 is thus steeredto the NMOS transistors T4 and T5. Since voltage level of the controlsignal 2 fo exceeds the reference voltage Vref at non-zero-crossingpoints of the local oscillator signal LO+/LO−, the NMOS transistors T3and T6 will be turned on. Current (both DC and AC) of the transconductorcell 350 is thus steered to the NMOS transistors T3 and T6. It iswell-known that flicker noise of the Gilbert cell mixer core 310 isproportional to a current injected therein at zero-crossing point.Therefore, steering current off the Gilbert cell mixer core 310according to the dynamic current steering cell of the present inventioncan successfully suppress the flicker noise and would be insensitive toLO quality.

FIG. 4C shows another embodiment of the dynamic current steering mixerof the present invention. The main difference between the dynamiccurrent steering mixer in FIG. 4A and in FIG. 4C is that the Gilbertcell mixer core 310 and the load devices are folded down and coupled tothe ground GND. The NMOS transistors T7, T8, T9 and T10 in the Gilbertcell mixer core 310 are replaced by PMOS transistors.

FIG. 4D shows another embodiment of the dynamic current steering mixerof the present invention. The main difference between the dynamiccurrent steering mixer in FIG. 4A and in FIG. 4D is that the NMOStransistors T7, T8, T9 and T10 in the Gilbert cell mixer core 310 arereplaced by bipolar junction transistors (BJTs). It is noted that theGilbert cell mixer core 310 and the load devices in FIG. 4D can also befolded down and coupled to the ground GND. In addition, the dynamiccurrent steering cell comprising the NMOS transistors T3, T4, T5, and T6is an embodiment and the scope is not limited thereto. Bipolar junctiontransistors are also applicable to the dynamic current steering cell.

FIG. 5A is a detailed circuit diagram of the dynamic current steeringmixer in FIG. 3. In FIG. 5A, the dynamic current steering cell 330comprises NMOS transistors T3, T4, T5 and T6. The NMOS transistors T3and T6 are coupled between the third nodes 331 and 331′ and the fourthnodes 333 and 333′. The NMOS transistors T4 and T5 are coupled betweenthe fixed voltage Vdd and the fourth nodes 333 and 333′. Gates of theNMOS transistors T3 and T6 are connected to a reference voltage Vref andthose of the NMOS transistors T4 and T5 receive the control signal 2 fo.Preferably, the fixed voltage Vdd is the same as the supply voltage Vcc.FIG. 5B is a schematic diagram showing waveforms of the local oscillatorsignal LO+/LO− and the control signal 2 fo in FIG. 5A. At zero-crossingpoints Toff of the local oscillator signal LO+/LO−, voltage level of thecontrol signal 2 fo exceeds the reference voltage Vref, allowing theNMOS transistors T3 and T6 to be turned off. Current (both DC and AC) ofthe transconductor cell 350 is thus steered to the NMOS transistors T4and T5. Since voltage level of the control signal 2 fo is lower than thereference voltage Vref at non-zero-crossing points of the localoscillator signal LO+/LO−, the NMOS transistors T3 and T6 are thenturned on. Current (both DC and AC) of the transconductor cell 350 isthus steered to the NMOS transistors T3 and T6. As a result, current ofthe transconductor cell 350 is steered off the Gilbert cell mixer core310 at zero-crossing points Toff of the local oscillator signal LO+/LO−and flicker noise thereof is thus suppressed.

FIG. 5C shows another embodiment of the dynamic current steering mixerof the present invention. The main difference between the dynamiccurrent steering mixer in FIG. 5A and in FIG. 5C is that the Gilbertcell mixer core 310 and the load devices are folded down and coupled tothe ground GND. The NMOS transistors T7, T8, T9 and T10 in the Gilbertcell mixer core 310 are replaced by PMOS transistors.

FIG. 5D shows another embodiment of the dynamic current steering mixerof the present invention. The main difference between the dynamiccurrent steering mixer in FIG. 5A and in FIG. 5D is that the NMOStransistors T7, T8, T9 and T10 in the Gilbert cell mixer core 310 arereplaced by bipolar junction transistors (BJTs). It is noted that theGilbert cell mixer core 310 and the load devices in FIG. 5D can also befolded down and coupled to the ground GND. In addition, the dynamiccurrent steering cell comprising the NMOS transistors T3, T4, T5, and T6is an embodiment and the scope is not limited thereto. Bipolar junctiontransistors are also applicable to the dynamic current steering cell.

FIG. 6A is a schematic diagram of current of a Gilbert cell mixer corein a conventional double balanced mixer and a dynamic current steeringmixer according to an embodiment of the invention. In FIG. 6A, currentof the Gilbert cell mixer core in a conventional double balanced mixerexceeds that of a dynamic current steering mixer according to anembodiment of the invention at zero-crossing points (represented by adashed-line box). FIGS. 6B and 6C are respectively schematic diagrams ofcurrent of the NMOS transistors in a Gilbert cell mixer core of aconventional double balanced mixer and a dynamic current steering mixeraccording to an embodiment of the invention. In FIG. 6B, current of theNMOS transistors in a Gilbert cell mixer core of a conventional doublebalanced mixer is about 1 mA. In FIG. 6C, current of the NMOStransistors in a Gilbert cell mixer core of a dynamic current steeringmixer according to an embodiment of the invention is only about 0.3 mA.FIG. 6D shows noise figure of a conventional double balanced mixer and adynamic current steering mixer according to an embodiment of theinvention. In FIG. 6D, noise figure of a conventional double balancedmixer is 15.3 dB at 10.4 kHz and that of a dynamic current steeringmixer according to an embodiment of the invention is only 12.3 dB at10.4 kHz.

FIG. 7A is a circuit diagram of a quadrature dynamic current steeringmixer according to an embodiment of the invention. In FIG. 7A, thequadrature dynamic current steering mixer 700 comprises an I-Quad mixer710 and a Q-Quad mixer 760. The I-Quad mixer 710 and the Q-Quad mixer760 are both dynamic current steering mixers as disclosed in FIG. 5A andconnected in parallel between a supply voltage Vcc and a ground GND. TheGilbert mixer core 310 in the I-Quad mixer 710 receives a localoscillator signal LOIP/LOIN and that in the Q-Quad mixer 760 a localoscillator signal LOQP/LOQN. The dynamic current steering cell 330 inthe I-Quad mixer 710 is controlled by a control signal 2LOP and that inthe Q-Quad mixer 760 controlled by a control signal 2LON. The I-Quadmixer 710 generates an IF signal IFIP/IFIN and the Q-Quad mixer 760 anIF signal IFQP/IFQN. Since the I-Quad mixer 710 and the Q-Quad mixer 760in the quadrature dynamic current steering mixer 700 are both dynamiccurrent steering mixers, noise figure of the quadrature dynamic currentsteering mixer 700 according to an embodiment of the invention is alsoimproved. It is noted that the disclosed variants of the dynamic currentsteering mixer in FIG. 4A and FIG. 5A can also be used in the quadraturedynamic current steering mixer.

FIG. 7B is a schematic diagram showing waveforms of the local oscillatorsignals LOIP/LOIN and LOQP/LOQN and the control signals 2LOP and 2LON.In FIG. 7B, at a zero-crossing point t1 of the local oscillator signalLOIP/LOIN, since voltage level of the control signal 2LOP exceeds thatof the reference voltage Vref, current Ia also exceeds current Ib.Meanwhile, voltage level of the reference voltage Vref also exceeds thatof the control signal 2LON, and current Id thus exceeds current Ic. Inother words, the currents Ia and Id consume most current atzero-crossing points of the local oscillator signal LOIP/LOIN and thecurrents Ib and Ic consume most current at zero-crossing points of thelocal oscillator signal LOQP/LOQN. As a result, current reuse isaccomplished by combining current Ia with Id, and combining Ic with Ib.

FIG. 8A is a circuit diagram of a variant of the quadrature dynamiccurrent steering mixer according to an embodiment of the invention. Thequadrature dynamic current steering mixer in FIG. 8A differs from thatin FIG. 7A only in that drains of the NMOS transistors TI3, TI4, TI5,and TI6 in the I-Quad mixer 710 are respectively connected with drainsof the NMOS transistors TQ4, TQ3, TQ6, and TQ5 in the Q-Quad mixer 760.Nodes A in FIG. 8A represent the drains of the NMOS transistors TI3 andTQ4 connected and nodes B in FIG. 8A represent the drains of the NMOStransistors TI4 and TQ3 are connected, and so forth. In suchconfiguration, dynamic current steering and current combination areachieved and noise figure and current consumption are thus improved.

FIG. 8B is a circuit diagram of a variant of the quadrature dynamiccurrent steering mixer in FIG. 8A, differing only in that the I-Quadmixer 810 and the Q-Quad mixer 860 are both dynamic current steeringmixer as disclosed in FIG. 4A.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. Alternatively, it is intended to cover variousmodifications and similar arrangements as would be apparent to thoseskilled in the art. Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

1. A mixer, comprising: a transconductor cell, receiving a differentialinput signal; a Gilbert cell mixer core, mixing the differential inputsignal with a differential oscillator signal to provide a differentialoutput signal; and a dynamic current steering cell, coupled between thetransconductor cell and the Gilbert cell mixer core, wherein the dynamiccurrent steering cell is arranged to selectively allow current flowingbetween the Gilbert cell mixer core and the transconductor cellaccording to a control signal.
 2. The mixer as claimed in claim 1,wherein frequency of the control signal is twice of that of thedifferential oscillator signal.
 3. The mixer as claimed in claim 1,wherein the dynamic current steering cell is arranged to not allow thecurrent flowing between the Gilbert cell mixer core and thetransconductor cell while the Gilbert cell mixer core is in a transientphase.
 4. The mixer as claimed in claim 3, wherein the Gilbert cellmixer core comprises differential pairs of transistors, and thedifferential pairs of transistors are switched from on-state tooff-state or from off-state to on-state during the transient phase. 5.The mixer as claimed in claim 1, wherein the dynamic current steeringcell is arranged to not allow the current flowing between the Gilbertcell mixer core and the transconductor cell at zero-crossing points ofthe differential oscillator signal.
 6. The mixer as claimed in claim 1,wherein the dynamic current steering cell comprises first transistorscoupled to the transconductor cell and the Gilbert cell mixer core andsecond transistors coupled to the transconductor cell and a firstvoltage, and wherein the first and second transistors respectivelyreceive one and the other of the control signal and a second voltage. 7.The mixer as claimed in claim 6, wherein the first transistors of thedynamic current steering cell are turned off while the Gilbert cellmixer core is in a transient phase.
 8. The mixer as claimed in claim 6,wherein the first transistors of the dynamic current steering cell areconfigured to be turned off in response to a voltage of the controlsignal being less than the second voltage, so as to prevent the currentfrom flowing between the Gilbert cell mixer core and the transconductorcell.
 9. A mixer, comprising: a transconductor cell, receiving adifferential input signal; a Gilbert cell mixer core, mixing thedifferential input signal with a differential oscillator signal toprovide a differential output signal; and a dynamic current steeringcell for steering current flowing between the Gilbert cell mixer coreand the transconductor cell according to a control signal of frequencybeing twice of that of the differential oscillator signal.
 10. The mixeras claimed in claim 9, wherein the dynamic current steering cell isarranged to selectively allow current flowing between the Gilbert cellmixer core and the transconductor cell according to the control signal.11. The mixer as claimed in claim 9, wherein the dynamic currentsteering cell comprises at least one switch which is arranged to preventthe current from flowing between the Gilbert cell mixer core and thetransconductor cell while the Gilbert cell mixer core is in a transientphase.
 12. The mixer as claimed in claim 11, wherein the Gilbert cellmixer core comprises differential pairs of transistors, and thedifferential pairs of transistors are switched from on-state tooff-state or from off-state to on-state during the transient phase. 13.The mixer as claimed in claim 9, wherein the dynamic current steeringcell is arranged to prevent the current from flowing between the Gilbertcell mixer core and the transconductor cell at zero-crossing points ofthe differential oscillator signal.
 14. The mixer as claimed in claim 9,wherein the dynamic current steering cell comprises first transistorscoupled to the transconductor cell and the Gilbert cell mixer core andsecond transistors coupled to the transconductor cell and a firstvoltage, and wherein the first and second transistors respectivelyreceive one and the other of the control signal and a second voltage.15. A method for dynamically steering current of a mixer, comprising thesteps of: receiving a differential input signal at an input stage;converting the differential input signal into a differential current;switching the differential current between outputs of a mixing unit at afrequency determined by a differential oscillator signal; and steeringthe differential current according to a control signal of frequencybeing twice of that of the differential oscillator signal.
 16. Themethod as claimed in claim 15, wherein the steering step furthercomprises: selectively allowing the differential current flowing betweenthe mixing unit and the input stage.
 17. The method as claimed in claim16, wherein the differential current is prevented from flowing betweenthe mixing unit and the input stage while the mixing unit is in atransient phase.
 18. The method as claimed in claim 17, wherein themixing unit comprises differential pairs of transistors, and thedifferential pairs of transistors are switched from on-state tooff-state or from off-state to on-state during the transient phase. 19.The method as claimed in claim 16, wherein the differential current isprevented from flowing between the mixing unit and the input stage atzero-crossing points of the differential oscillator signal.
 20. Themethod as claimed in claim 15, further comprising: coupling a firstvoltage to the input stage so as to prevent the differential currentfrom flowing between the mixing unit and the input stage when a voltageof the control signal is lower than a second voltage; and coupling themixing unit to the input stage so as to allow the differential currentflowing between the mixing unit and the input stage when the voltage ofthe control signal is not lower than the second voltage.